Electrical Instruments in Hazardous Locations Book

	Preface	xi
Chapter 1	Historical Background and Perspective	1
	Growing Interest in the Safety of Electrical Instrument Installations	1
	The Role of Underwriting and Standards Developing Organizations	3
	Occupational Safety and Health Administration	12
	Progress in Electrical Safety Standards Development	14
	References	14
Chapter 2	Combustion and Explosion Fundamentals	17
	Some Underlying Theory	17
	Ignition By a Point Source	21
	Ignition Energy and Flame Velocity	28
	Lower and Upper Explosive Limits	29
	Most Easily Ignited Concentration	31
	Minimum Ignition Energy	32
	Effect of Test Conditions	32
	Effect of Changing Inert Gases	38
	Electrode Geometry	39
	Time Scale of the Ignition Process	40
	References	41
Chapter 3	Classification of Hazardous Locations and Combustible Materials	43
	Why Area Classification?	43
	The North American System	43
	Classes and Groups of Materials	44
	Determination of Area Classification Relative to Class I Hazards	49
	Considerations in Classification of Class I Locations	51
	Some Guides for Class I Area Classification	55
	Special Cases of Area Classification in Instrument Systems	58
	Area and Material Classification Outside the United States	60
	Material Classification in the United States--Tutorial Discussion and Opinion	75
	References	94
Chapter 4	Practice and Principles of Hazard Reduction Practice	99
	United States	99
	Canada	102
	Countries Following IEC or CENELEC Standards	102
	The Types of Protection	103
	Principles	108
	References	134
Chapter 5	Explosionproof Enclosures	137
	Why an Explosionproof Enclosure Works	137
	Influence of Enclosure Design and Test Procedure	139
	Pressure Piling	153
	Correlation Between MESG and Spark Ignition Energy	157
	Design Criteria--Introduction	159
	References	176
Chapter 6	Reduction of Hazard by Pressurization	183
	Recognition in the National Electrical Code	183
	The Standardization of Pressurization	184
	Classification of Pressurization Systems	186
	NFPA 496 Requirements for Pressurization Systems	187
	Additional Requirements for Pressurized Enclosures in Class I Locations	192
	Requirements for Pressurized Enclosures in Class II Locations	193
	Requirements for Pressurized Control Rooms	193
	Pressurization of Enclosures with Internal Source of Release--Continuous Dilution	194
	Cenelec EN50016	204
	Installation of Pressurization Systems	211
	References	215
Chapter 7	Encapsulation, Sealing, and Immersion	217
	Oil and Sand Immersion	217
	Sealing	219
	Defining Safety Requirements for Sealed Devices	229
	Standards for Sealed Devices	235
	Encapsulation or Potting	244
	References	247
Chapter 8	Increased Safety, Type of Protection e	251
	Construction Requirements	253
	Creepage and Clearances	254
	References	263
Chapter 9	Ignition of Gases and Vapors by Electrical Means	265
	Characteristics of Electric Arcs	267
	Arcing at Closing Contacts and in Capacitive Circuits	274
	Typical Test Equipment for Capacitive Circuits	278
	Precautions in Testing	281
	Typical Ignition Test Results	284
	Effect of Resistance in Discharge Path	286
	Effects of Electrode Material and Geometry	294
	Opening Contacts in Inductive and Resistive Circuits	294
	Test Equipment for Break-Spark Ignition Measurements	296
	Influence of Contact Material	299
	Effect of Contact Separation Speed	306
	Ignition of Materials Other than Methane	307
	Probability of Ignition--Influence of Current and Voltage Level	311
	Effect of Shunt Elements on Ignition Current	315
	Hot Wire Ignition	324
	References	335
Chapter 10	Intrinsically Safe and Nonincendive Systems	341
	Historical Review	341
	Interpreting the Definition	345
	Specific Requirements for Intrinsically Safe Systems	349
	Requirements for All Intrinsically Safe Apparatus	354
	Requirements for Features and Components on which Intrinsic Safety Depends	359
	Requirements for Infallible (Protective) Components, Infallible Assemblies, and Infallible Connections	367
	How Safe is Safe?	374
	Installation of Intrinsically Safe Systems	394
	Inspection of Intrinsically Safe Systems	400
	Maintenance of Intrinsically Safe Systems	404
	Nonincendive Equipment and Wiring	406
	References	410
Chapter 11	Design and Evaluation of Intrinsically Safe Apparatus, Intrinsically Safe Systems, and Nonincendive Systems	415
	Design and Evaluation of Intrinsically Safe Apparatus	415
	Power Supplies	428
	Inductors with Ferromagnetic Cores	433
	Zener Diode Track Layout	461
	Design of Intrinsically Safe Systems	469
	References	489
Chapter 12	Ignition by Optical Sources	493
	Overview	493
	Ignition by Radiating Sources	497
	The Nature of the Hazard	507
	Standards Actions to Address Hazards of Radiation - Opinions of the Author	516
	Need for Further Study and Research	517
	References	518
Chapter 13	Dust Hazards	521
	Nature of the Dust Hazard	521
	Influence of Chemical Composition of the Dust	523
	Influence of Shape, Size, and Concentration	527
	Chemical Composition of the Suspending Medium	529
	Distinguishing Features of Dust Hazards	531
	Area Classification	533
	Electrical Apparatus For Dusty Locations	538
	Ways to Reduce Hazard	541
	IEC and CENELEC	541
	References	544
Chapter 14	Human Safety	547
	Introduction	547
	Effects of Electrical Shock	547
	The Body as a Circuit Element	550
	What is a Safe Level of Circuit Voltage?	553
	Conclusion	554
	References	554
Chapter 15	Degree of Protection by Enclosures	555
	The NEMA System	555
	IEC 529	558
	Correlation of NEMA and IP Codes	562
	References	562
Appendix A	Derivation of Initial Purge Volume Requirement	563
Appendix B	Examples of Derivations	567
	Derivation of an Equation for Loss of Pressure in a Sealed System	567
	Derivation of Expressions for Seal Breathing	569
	Derivation of Expressions for Pressure Testing Sealed Enclosures	572
	Derivation of Flow Test Equation	574
	Index	575